In general, to manufacture an electrolytic copper foil, a rotating metal cathode drum having a polished surface and an insoluble metal anode that goes around the periphery of approximately the lower half of the cathode drum are used, and a copper electrolytic solution is made to flow between the cathode drum and the anode. A potential is also applied between the cathode drum and the anode, whereby copper is electrodeposited onto the cathode drum. Once the electrodeposited copper has reached a prescribed thickness, the electrodeposited copper is peeled off from the cathode drum, whereby copper foil is manufactured continuously.
Copper foil obtained in this way is generally referred to as raw foil. This raw foil is subsequently subjected to various surface treatment and is then used in printed wiring boards or the like.
A conventional copper foil manufacturing apparatus is shown schematically in FIG. 1. In this electrolytic copper foil apparatus, a cathode drum is installed in an electrolysis bath housing an electrolytic solution. The cathode drum 1 rotates in a state partially submerged (i.e. with approximately the lower half submerged) in the electrolytic solution.
An insoluble anode 2 is provided so as to go around the lower half of the outer periphery of the cathode drum 1. There is a constant gap 3 between the cathode drum 1 and the anode 2, and the electrolytic solution flows through this gap. In the apparatus of FIG. 1, two anode plates are used.
In FIG. 1, the constitution is such that the electrolytic solution is fed in from below, passes through the gap 3 between the cathode drum 1 and the anode 2, and flows over upper edges of the anode 2, thus circulating. A prescribed voltage is maintained between the cathode drum 1 and the anode 2 using a rectifier.
As the cathode drum 1 rotates, the copper electrodeposited from the electrolytic solution grows thicker, and once the copper has become at least a certain thickness, the raw foil 4 is peeled off, and is wound up continuously. The thickness of the raw foil manufactured in this way is adjusted through the distance between the cathode drum 1 and the anode 2, the flow rate of the electrolytic solution fed in, and the amount of electricity fed in.
With copper foil manufactured using such an electrolytic copper foil manufacturing apparatus, the surface contacting the cathode drum becomes a specular surface, but the surface on the other side becomes a rough surface having irregularities. With ordinary electrolysis, the irregularities on the rough surface are severe, and hence there is a problem that undercutting is prone to occurring during etching, and thus fine patterning is difficult.
However, recently, as the density on printed wiring boards has been increased, the circuit width has been reduced and the number of layers has been increased, and accompanying this copper foil that can be finely patterned has come to be required. To carry out fine patterning, copper foil having crystal grains of a uniform size and having a uniform etching rate and a uniform solubility, i.e. copper foil having excellent etching properties, is required.
Moreover, regarding properties required of copper foil for printed wiring boards, not only elongation at normal temperatures, but also elongation at high temperatures are required to prevent cracking due to thermal stress. Furthermore, high tensile strength for dimensional stability of printed wiring boards are required. However, copper foil for which irregularities on the rough surface are severe as above causes a problem of not being suited to fine patterning at all as described above. Studies have thus proceeded into making the rough surface have a low profile.
It is known that, in general, a low profile can be achieved by adding a large amount of animal glue or thiourea to the electrolytic solution. However, such additives have a problem of causing the elongation percentage to drop dramatically at normal and high temperatures, thus causing a great deterioration in the properties as a copper foil for printed wiring boards.